The present invention relates to a servo data writing device which writes servo data for positioning a magnetic head for writing and reading data on a magnetic disk of a magnetic disk drive unit.
Magnetic disks are assembled in a magnetic disk drive unit. A plurality of tracks are coaxially formed in each magnetic disk. Servo data are magnetically written in each sector of each track. The servo data are used to position magnetic heads in object tracks.
When the servo data are written in the magnetic disk, no servo data have been written in the magnetic disk, so the magnetic disk drive unit cannot position its own magnetic head.
For example, the magnet disk drive unit is assembled by the steps of: assembling a motor for rotating a spindle; attaching magnetic disks to the spindle; assembling an inner actuator, which has arms for holding the magnetic heads and moves the magnetic heads in the radial direction of the magnetic disks; and attaching the magnetic heads to the arms. The magnetic disk drive unit, whose arms, magnetic disks and magnetic heads are accessible from outside, is attached to a servo data writing device so as to write the servo data. Note that, the state of “accessible from outside” means that a state in which the magnetic disk drive unit is not accommodated in a chassis, a state in which the magnetic disk drive unit is accommodated in the chassis piece but element members therein can be accessible from outside, etc.
For example, as shown in FIGS. 6 and 7, a conventional servo data writing device includes: an external actuator 58 capable of positioning arms 56 of an inner actuator 54 of a magnetic disk drive unit 52 from outside; a position sensor 60 for detecting a present position of the external actuator 58; an external actuator control circuit 64 capable of positioning the external actuator 58 with the position sensor 60 and positioning magnetic heads 62, which is held by the arms 56, in prescribed tracks; a pattern generating circuit 66 for generating the servo data, which are written in a predetermined position in each sector of each track; a first write-read control circuit 68 capable of writing the servo data in magnetic disks 70 with the magnetic heads 62, which is provided in the magnetic disk drive unit 52; a clock head 74 capable of recording reference clock signals, which are synchronized with rotation of a spindle 72 and the magnetic disks 70, in clock recording areas, which are, for example, respectively provided in outer edges of the magnetic disks 70, and reproducing the reference clock signals; a second write-read control circuit 76; a driving mechanism 78 of the clock head 74; a spindle motor 80 for rotating the spindle 72; and a motor control circuit 82 capable of rotating the spindle 72 at prescribed rotational speed.
A host computer 84, which is provided in the servo data writing device 50, controls structural elements of the servo data writing device 50.
Action of the servo data writing device 50 will be explained. Firstly, the motor control circuit 82 rotates the motor 80 to continuously rotate the magnetic disks 70 at prescribed rotational speed. Next, the reference clock signals are written in the clock recording areas of the magnetic disks 70 with the clock head 74 and the second write-read control circuit 76. The external actuator control circuit 64 positions the external actuator 58 so as to position the magnetic heads, which are held by the arms 56, in object tracks with the position sensor 60. For example, the external actuator 58 positions the arms 56 of the inner actuator 54 by pushing a pin of the external actuator 58. The pin (not shown) of the external actuator 58 is pressed onto the arms 56 of the inner actuator 54 of the magnetic disk drive unit 52 and moved.
When the magnetic heads 62 are positioned in the object track in which the servo data are written, the pattern generating circuit 66 receives the reference clock signals, which are reproduced by the clock head 74, as clock signals and generates the servo data. The servo data are inputted to the magnetic heads 62 via the first write-read control circuit 68, and the servo data are written in the magnetic disks 70.
Note that, frequency of standard clock signals, which are inputted to the pattern generating circuit 66, is generally higher than that of the reference clock signals reproduced by the clock head 74 so as to generate the servo data from the pattern generating circuit 66. Thus, a PLL circuit (not shown) is provided inside or outside of the pattern generating circuit 66. The reference clock signals are inputted to the PLL circuit as clock signals so as to make the standard clock signals for generating the servo data. The frequency of the standard clock signals is integral number times as high as that of the reference clock signals.
The servo data, which are generated from the pattern generating circuit 66, in the sectors must be mutually different even if the sectors are in the same track. The servo data are written at a predetermined position in each sector, and the servo data recorded positions in the sectors must be corresponded. So, the pattern generating circuit 66 generates the start pulse, which is synchronized with the servo data recorded position, on the basis of the reference clock signals, which are changed according to the rotation of the magnetic disks 70, and the servo data for each sector are synchronously generated with the start pulse. The rotational speed of the magnetic disks 70 is controlled at fixed speed, so the start pulses, whose number is equal to number of the sectors in one track, are generated at regular intervals while one magnetic disk 70 makes one rotation.
However, the conventional servo data writing device has following disadvantages.
Firstly, the conventional servo data writing device 50 should have the external actuator 58 and the external actuator control circuit 64, which correspond to the magnetic disk drive unit to be attached, as positioning means. And, the clock head 74, the second write-read control circuit 76, the driving mechanism 78 and the first write-read control circuit 68 should be required so as to write the servo data in the magnetic disks and to read the same therefrom.
Therefore, the system of the servo data writing device 50 must be huge and the body of the device 50 must be large and heavy. These days, the technology of the magnetic disk has been highly advanced, and the magnetic disk drive units are frequently improved. Hardware of the servo data writing device having huge system must be frequently changed when the type of the magnetic disk drive unit is changed, so that manufacturing cost must be higher, and extra work takes time uneconomically.
Secondly, in the conventional servo data writing device, the servo data are recorded at the predetermined position of each sector of each track, and the the servo data recorded positions in the sectors are mutually corresponded, as described above. Thus, in the conventional device 50, firstly the reference clock signals are written in the clock recording areas of the magnetic disks 70 with the clock head 74.
When the servo data are written in the tracks, the reference clock signals are reproduced by the clock head 74, the start pulse synchronized with the reference clock signals is generated on the basis of the reference clock signals, and the servo data of each sector is synchronously generated with the start pulse. Further, the standard clock signals, whose frequency is higher than that of the reference clock signals, are generated on the basis of the reference clock signals, and the servo data are generated from the pattern generating circuit 66 on the basis of the standard clock signals.
In the mean time, the PLL circuit receives the reference clock signals and generates the standard clock signals having higher frequency. Therefore, duty ratio of the reference clock signals should be fixed. If the duty ratio is not fixed, the PLL circuit does not correctly work and the standard clock signals are stopped. When a record starting point of the reference clock signals and a record terminating point thereof are not smoothly connected by the clock head, the duty ratio is not fixed. Conventionally, the action of writing the reference clock signals must be repeated many times until the points are smoothly connected.